1. Field of the Invention
The present invention relates to improved methods and apparatus for completing wells in unconsolidated subterranean zones, and more particularly, to improved methods and apparatus for completing such wells whereby the migration of fines and sand with the fluids produced therefrom is prevented.
2. Description of the Prior Art
Oil and gas wells are often completed in unconsolidated formations containing loose and incompetent fines and sand which migrate with fluids produced by the wells. The presence of formation fines and sand in the produced fluids is disadvantageous and undesirable in that the particles abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones in the wells.
Heretofore, unconsolidated subterranean zones have been stimulated by creating fractures in the zones and depositing particulate proppant material in the fractures to maintain them in open positions. In addition, the proppant has heretofore been consolidated within the fractures into hard permeable masses to reduce the migration of formation fines and sands through the fractures with produced fluids. Further, gravel packs which include sand screens and the like have commonly been installed in the well bores penetrating unconsolidated zones. The gravel packs serve as filters and help to assure that fines and sand do not migrate with produced fluids into the well bores.
In a typical gravel pack completion, a screen is placed in the well bore and positioned within the unconsolidated subterranean zone which is to be completed. The screen is typically connected to a tool which includes a production packer and a cross-over, and the tool is in turn connected to a work or production string. A particulate material which is usually graded sand, often referred to in the art as gravel, is pumped in a slurry down the work or production string and through the cross-over whereby it flows into the annulus between the screen and the well bore. The liquid forming the slurry leaks off into the subterranean zone and/or through the screen which is sized to prevent the sand in the slurry from flowing therethrough. As a result, the sand is deposited in the annulus around the screen whereby it forms a gravel pack. The size of the sand in the gravel pack is selected such that it prevents formation fines and sand from flowing into the well bore with produced fluids.
A problem which is often encountered in forming gravel packs, particularly gravel packs in long and/or deviated unconsolidated producing intervals, is the formation of sand bridges in the annulus. That is, non-uniform sand packing of the annulus between the screen and the well bore often occurs as a result of the loss of carrier liquid from the sand slurry into high permeability portions of the subterranean zone which in turn causes the formation of sand bridges in the annulus before all the sand has been placed. The sand bridges block further flow of the slurry through the annulus which leaves voids in the annulus. When the well is placed on production, the flow of produced fluids is concentrated through the voids in the gravel pack which soon causes the screen to be eroded and the migration of fines and sand with the produced fluids to result.
In attempts to prevent the formation of sand bridges in gravel pack completions, special screens having internal shunt tubes have been developed and used. While such screens have achieved varying degrees of success in avoiding sand bridges, they, along with the gravel packing procedure, are very costly.
Thus, there are needs for improved methods and apparatus for completing wells in unconsolidated subterranean zones whereby the migration of formation fines and sand with produced fluids can be economically and permanently prevented while allowing the efficient production of hydrocarbons from the unconsolidated producing zone.
The present invention provides improved methods and apparatus for completing wells, and optionally simultaneously fracture stimulating the wells, in unconsolidated subterranean zones which meet the needs described above and overcome the deficiencies of the prior art. The improved methods basically comprise the steps of placing a slotted liner having an internal sand screen disposed therein whereby an annulus is formed between the sand screen and the slotted liner in an unconsolidated subterranean zone, isolating the annulus between the slotted liner and the well bore in the zone, injecting particulate material into the annulus between either or both the sand screen and the slotted liner and the liner and the zone by way of the slotted liner whereby the particulate material is uniformly packed into the annuli between the sand screen and the slotted liner and between the slotted liner and the zone. The permeable pack of particulate material formed prevents the migration of formation fines and sand with fluids produced into the well bore from the unconsolidated zone.
As mentioned, the unconsolidated formation can be fractured prior to or during the injection of the particulate material into the unconsolidated producing zone, and the particulate material can be deposited in the fractures as well as in the annuli between the sand screen and the slotted liner and between the slotted liner and the well bore.
The apparatus of this invention are basically comprised of a slotted liner having an internal sand screen disposed therein whereby an annulus is formed between the sand screen and the slotted liner, a cross-over adapted to be connected to a production string attached to the slotted liner and sand screen and a production packer attached to the cross-over.
The improved methods and apparatus of this invention avoid the formation of sand bridges in the annulus between the slotted liner and the well bore thereby producing a very effective sand screen for preventing the migration of fines and sand with produced fluids.
It is, therefore, a general object of the present invention to provide improved methods of completing wells in unconsolidated subterranean zones.